Bags with mouth members are used for medical containers such as infusion bags, food containers with a spout, and the like. In the field of medical containers, use of medical containers comprising synthetic resin instead of conventional glass-made medical containers has increased. Synthetic resin-made medical containers include containers produced by blow molding, and bag-like containers made by using a flexible film which is produced by inflation or T-die molding. In particular, the case of using bag-like containers produced from flexible film is increasing.
This is because, for example, bag-like containers made by using a flexible film have a thin and uniform wall thickness enabling reduction of volume after use and in turn reduction of waste, the infusion solution is discharged at an almost constant rate until the last on transfusing the content, and when the liquid is reduced, the volume of container can be reduced without allowing the invasion of air and, therefore, can be kept free from contamination with miscellaneous bacteria due to air. FIG. 8 shows, as an example of a medical container used at present, an infusion solution bag being a bag with a mouth member, wherein a bag unit comprises a flexible film 2 for housing a medical liquid and a hollow cylinder 1 shown in FIG. 9 working as a mouth member for filling or discharging the medical liquid which are fixed by interposing the mouth member 1 between two film sheets 21 of the bag unit and heat-bonding these.
In a bag with a mouth member, for fixing the mouth member to the film, a three-dimensionally shaped mouth member must be liquidtightly fixed to a two-dimensional planar film and, as shown in FIG. 10, an A-shaped gap 22 is sometimes generated between the two film sheets and the melt-bonding part of the mouth member (hereinafter, this gap is referred to as an “A-shaped gap”) causing leakage of the liquid content. Particularly, in the case of a thick film having a film thickness of 100 μm or more, even though the film is deformed in agreement with the shape of the mouth member at the time of the melt-bonding under heat, the melt-bonded portion sometimes become separated due to the restoring stress of the film. Furthermore, on melt-bonding the mouth member and the film by sandwiching these with a sealing mold, the film may be subject to excess tensile stress in making it match the shape of the mouth member and this bears a risk of thinning the film or forming a hole in the film.
For preventing such deformation or hole formation in the film due to heat, a method of stacking a heat-resistant layer on the film via an adhesive and using the resulting laminate film enhanced in heat resistance, and a method of fixing the film and the mouth member with use of an adhesive are known. However, the adhesive sometimes dissolves out and its use is not preferred in the medical field. Accordingly, there is demand for integration of the film and the mouth member directly by melt-bonding.
The melt-bonding of a mouth member to a bag unit is performed by inserting the mouth member into the opening part of the bag unit and externally pressing these under heat. However, when pressed under heat, the flexible film of the bag unit melts, due to elevation of the temperature, earlier than the mouth member and is readily thinned and thus the thinning of the flexible film causes a decrease in the drop strength of bag, easy formation of pinholes and in turn a reduction in the productivity when manufacturing the bag with a mouth member.
As a method for liquidtightly melt-bonding a bag unit comprising a flexible film and a mouth member without generating an A-shaped gap in order to improve productivity, a method of melt-bonding the film by using a heated mouth member is known.
In the preheating step of the mouth member, the heating must be performed to make the surface temperature of the mouth member uniform so that a resin in an amount sufficiently large to fill the A-shaped gap can be melted and extended from the mouth member to the space between films to unfailingly prevent liquid leakage when the mouth member is melt-bonded with a film in a later step, so that the seal strength between the mouth member and the film can be uniform, and so that the mouth member can be prevented from thermal deformation.
As for the technique of heating a mouth member, a technique of melt-bonding the mouth member by heating it with radiant heat is disclosed (see, for example, Patent Document 1).
According to the method described in Patent Document 1, the surface layer in the melt-bonding part of a mouth member is heated at a temperature from the softening point of the material in the melt-bonding part of the mouth member to a temperature 13° C. higher than the melting point by using radiant heat of a heater at a temperature of 600 to 800° C. in advance of melt-bonding the mouth member to a film, the heated mouth member is pressed from both sides by thin strip-shaping molds symmetrical with respect to the mouth member to shape a fin-like thin strip, the mouth member maintained in the heated state is inserted between films, and the mouth member is melt-bonded to the film by using a heat-sealing mold. As for the heater used here for heating, in the case where the mouth member has a complete round shape, a ring-like heater having a diameter several mm larger than the diameter of the melt-bonding part of the mouth member is used.
In the method for the preheating step described in Patent Document 1, the radiant heating must be performed by disposing the ring-like heater and the cylindrical mouth member so that the center of the ring matches with the cylinder axis, so that the melt-bonding part surface of the cylindrical mouth member can be uniformly heated.
In this method, for elevating the heating efficiency, the inner diameter of the ring-like heater is made larger by at least about 2 to 3 mm than the outer diameter of the melt-bonding part of the cylindrical mouth member, and this amounts to an inner diameter of about 10 to 30 mm as estimated from the size of commonly employed cylindrical mouth members. Such a small ring-like heater readily has unevenness in the temperature distribution of the heat generating part and even when the cylinder axis of the cylindrical mouth member and the center of the ring-like heater are matched, the surface temperature of the mouth member is not necessarily uniform. In general, an operation of subtly adjusting the relative positions of the mouth member and the ring-like heater and deciding the positions while observing the melted state of the mouth member surface with the eye is necessary and this requires a great deal of labor and time, and further requires much skill.
If this operation is improper, a non-uniform temperature distribution results on the mouth member surface, as a result, there arise many fatal failures such as liquid leakage due to non-uniform flow of the melted resin into the A-shaped gap from the mouth member in the later step, separation or bag breakage due to local reduction of the film melt-bonded strength, and deformation of the mouth member due to partial melting or unbalanced thermal expansion thereof. Also, if the surface temperature of the mouth member becomes excessively high, defective mouth member resin may be generated and this defective product may be fitted into the melt-welding part and cause liquid leakage or may intrude into the bag.
Accordingly, securing a uniform surface temperature of the mouth member in the preheating step is a very important factor for ensuring stable production of a high-quality bag with a mouth member and the realization of easily and reliably of a uniform surface temperature of the mouth member is a major goal.
Patent Document 1: Japanese Patent No. 3048486